FIG. 1 shows a configuration example of a liquid crystal display for displaying images, which constitutes a computer terminal, a mobile electronic device or a television receiver.
A liquid crystal display panel 2 is constituted by sealing liquid crystals between two polarizing plates (not shown), and displays images by changing directions of liquid crystal molecules by applying voltage to vary light transmissivity. Since the liquid crystals themselves of the liquid crystal display panel 2 do not emit light, a backlight apparatus 1 performs surface emission from the back side of the liquid crystal display panel 2.
This backlight apparatus 1 is configured with LED devices 11B, 11G and 11R as light sources (hereinafter, they are referred to simply as an LED device 11 when it is unnecessary to individually differentiate between them. They are referred to in a similar way also in other cases), a light guiding plate 12, a diffusion sheet 13, a BEF sheet 14 and a D-BEF seat 15, which are stacked one after the other as shown in the figure and disposed so as to oppose the liquid crystal display panel 2, and performs surface emission toward the liquid crystal display panel 2.
As the light sources of the surface emission, the LED devices 11B, 11G and 11R of the backlight apparatus 1 emit blue light Lb, green light Lg, red light Lr, respectively. As shown in FIG. 2, the blue light Lb, the green light Lg and the red light Lr emitted from the LED device 11 are naturally mixed and becomes white light Lw while being led by the light guiding plate 12.
In the example of FIG. 1, there is provided only one for each of the LED devices 11B, 11G, 11R respectively emitting the blue light Lb, the green light Lg, the red light Lr, for simplicity, however, practically, a plurality of respective LED devices 11B, 11G, 11R are provided in a predetermined ratio.
As shown in FIG. 2, the light guiding plate 12 guides the light entered through a light guide path 12A and a reflection path 12B to the diffusion sheet 13 disposed on the top surface of the light guiding plate 12.
The light guiding path 12A and the reflection path 12B are designed to have a space necessary for naturally mixing the light emitted from the LED devices 11B, 11G and 11R to become the white light Lw. For example, a width W and a diameter R in FIG. 2 are set to predetermined dimensions enough for forming such space. In addition, materials of the light guiding path 12A and the reflection path 12B are predetermined materials so that the light is reflected with a suitable refraction index for performing light guiding or reflection efficiently.
The light guiding plate 12 has a bottom portion on which, for example, dots are formed in order to exit light to each portion of the diffusion sheet 13 as uniformly as possible, so that some of the guided light is reflected by the dots and exited to the diffusion sheet 13 side.
The diffusion sheet 13 is made of, for example, a polycarbonate film of 0.25 mm in thickness, uniforms the light entered from the light guiding plate 12 by diffusing ununiformed part thereof, and transmits the resultant light to the BEF sheet 14.
A BEF (Brightness Enhancement Firm) sheet (brightness improvement sheet for P-component: the BEF series is a product name of Sumitomo 3M company) 14 converges the P-component beyond a viewing angle of the liquid crystal of the liquid crystal display panel 2 (a visible angle for a user, of the light transmitted through the liquid crystal display panel 2) among the P-component of the light entered through the diffusion sheet 13 to within the viewing angle. Since the light (P-component) beyond the viewing angle of the liquid crystal display panel 2, which is invisible for a user even passed through the liquid crystal display panel 2, is to be converged within the viewing angle in this manner, apparent brightness can be improved. It is to be noted that, an S-component of the light entered to the BEF sheet is transmitted to the D-BEF sheet 15 as it is.
The D-BEF sheet (brightness improvement sheet for S-component) 15 converts the S-component of the light entered through the BEF sheet 14 into the P-component and, as similar to the BEF sheet 14, converges the P-component light beyond the viewing angle of the liquid crystal display panel 2, and transmits the converged light to the liquid crystal display panel 2.
The liquid crystal display panel 2 (FIG. 1) is originally configured to transmit only the P-component by the polarizing plate. In response to a signal from a not shown signal line, the liquid crystal display panel 2 controls directions of the liquid crystals by each pixel unit and varies the transmission amount of the white light Lw which is formed by the light generated from the LED device 11 and entered via the light guiding plate 12, the diffusion sheet 13, the BEF sheet 14 and the D-BEF sheet 15 to form and display images.
It is to be noted that, in addition to the example of FIG. 1, an example of a backlight apparatus having an LED device as a light source which naturally mixes blue light, red light and green light emitted from the LED device is disclosed in Utility Model Publication No. Hei 7-36347 and JP-T 2002540458.
[Patent Document 1] Utility Model Publication No. 7-36347, JP-T 2002540458.